Display Dell U4021qw scrambled into strange tiles

Screenshot Ok says the data are correct in RAM. Either the display resolution has been set to something 'out-of-bounds' or a rasterizer/display generator has failed.

Let's assume the former, since BOTH displays went wonky. When you start in Safe Mode, it sets the display resolutions using defaults. BUT -- Any changes you make in Safe Mode will 'stick' in regular mode. This is a recommended way to recover from wonky screen resolutions that preclude further modification because the screen 'breaks up' like yours did.

so Restart in Safe Mode, then change the screen resolution part way toward what you want. if it breaks up again and won't go back after minute or two, you can restart in safe mode again to get the defaults again.

One more tip I want you to take with you:

To toggle the sense of [√] Mirror displays, use shortcut:

Command-BrightnessDown

Hi,

If that can help someone...

I had the same issue (where both the built-it screen and the U4021qw were displaying strange tile/scrambled as on your picture posted below in the thread) when my MacBook Pro (13-inch, 2019, Two Thunderbolt 3 ports) was running on Ventura (13.2.1). When starting in safe mode I was able to get the Dell monitor working but as soon as I started in normal mode the issue popped up again.

What I tried without success:

• uninstall several apps
• reinstall MacOS Ventura (with disc format)
• reinitialize RAM
• reset Monitor
• update Dell Monitor to firmware M2T104 & M2T105

I finally got the monitor perfectly working by installing Monterey (verison 12.6.3).

Specs of the MacBook Pro:

MacBook Pro (13-inch, 2019, Two Thunderbolt 3 ports)

CPU 1.7 GHz Quad-Core Intel Core i7

Memory 16GB 2133 Mhz LPDDR3

Graphics : Intel Iris Plus Graphics 645 1536MB

Hi, I have the exact same issue when connecting my Dell U4021qw display to my 2020 MBP (Intel processor).

I've tried all the steps in this thread to no avail, with the exception of downgrading OS back to Monterey, which I can't do as it's a work laptop.

I did find a partial solution as follows in case it helps anyone else:

• restart MPB in safe mode (where both screens will work without the scrambled lines)
• on the dell display, navigate in the display setting to PIP/PBP
• turn on PIP/PBP mode and select 80%-20%
• restart the MPB
• the scrambling should be gone (but you will only be able to use 80% of your dell display)

This will keep me going until someone diagnoses the full issue!

that is wrong resolution or failure to sync up properly.

That the built-in next to it has a similar repeating pattern is a very important part of the diagnosis.

This is most likely a problem in the computer, not in the display.

see if it happens in Safe Mode, which takes all the defaults and uses a lower resolution (but if you change resolution while in Safe Mode, the changes will stick in regular mode).

This may be tough, but you could try taking a screenshot to see if the artifacts appear in the screenshot as well. if they do appear in the screenshot, wrong stuff was written into the screen buffer of its RAM failed.

Your MacBook Pro 13-in Touch Bar from 2019 uses Iris Plus graphics that shares system memory, no separate display memory.

did you try the approach labeled "Best Answer" above, and summarized here:

When you start in Safe Mode, it sets the display resolutions using defaults. BUT -- Any changes you make in Safe Mode will 'stick' in regular mode. This is a recommended way to recover from wonky screen resolutions that preclude further modification because the screen 'breaks up' like yours did.

so Restart in Safe Mode, then change the screen resolution part way toward what you want. if it breaks up again and won't go back after minute or two, you can restart in safe mode again to get the defaults again.

Hi,

this did unfortunately not work for my setup. In safe mode the display was working correctly (on Ventura) but as soon as it started in normal mode the issue was happening again (even after formatting and reinstalling Ventura from scratch).

the issue is not there on Monterey, the display is working fine.

Best regards

Your description does not sound like what I recommended. so let me restate what I was trying to get you to do.

In safe mode, make a deliberate but modest adjustment of the starting default resolution, and try it for a little while in safe mode. That same resolution should "stick' in regular mode.

Then restart in regular mode. Try for a little while.

if still working, do the same procedure again: in safe mode, make a more aggressive move toward the ultimate desired resolution. run for a little while. restart in regular mode.

Were you able to solve the issue in the meantime? I have the same problem.

Can you take a photo with your iPhone and post the photo?

What graphic card does your MBP has? Intel iris 645 as well?